Cathepsin K and cathepsin S are members of the papain family, within the papain superfamily of cysteine proteases. The papain family is the largest group of cysteine proteases and includes proteases such as cathepsins B, H, K, L, O and S. (A. J. Barrett et al., 1996, Perspectives in Drug Discovery and Design, 6, 1). The cysteine proteases have important roles in human biology and diseases including osteoporosis, chronic inflammation and immune disorders, atherosclerosis, and emphysema (H. A. Chapman et al., 1997, Ann. Rev. Physiol., 59, 63). Cysteine proteases are also involved in the pathogenesis of some infectious diseases, including malaria (A. Semenov et al., Antimicrobial Agents and Chemotherapy, 1998, 42, 2254) and Chagas' disease, (J. C. Engel et al., J. Exp. Med., 1998, 188, 725). Bacterial cysteine proteases contribute to the pathogenesis of gingivitis (J. Potempa et al., Perspectives in Drug Discovery and Design, 1994, 2, 445).
Cathepsin K has been found to be highly expressed in osteoclasts, cells involved in bone resorption (F. H. Drake et al., J. Biol. Chem., 1996, 271, 12511). Collagen and osteonectin, two protein components of bone matrix have been found to be substrates of activated cathepsin K (M. J. Bossard et al., J. Biol. Chem., 1996, 271, 12517). Inhibitors of cathepsin K have been shown to have anti-resorptive activity in vitro and in vivo (S. K. Thompson et al., Proc. Natl. Acad. Sci. USA, 1997, 94, 14249). The essential role of cathepsin K in bone resorption has also been confirmed in cells and organisms lacking this protease. At the cellular level, cathepsin K deficient osteoclasts, when tested for functional activity on dentine, produced fewer resorption pits as compared to wild-type osteoclasts (P. Saftig et al., Proc Natl Acad Sci USA 1998, 95,13453). Cathepsin K knockout mice develop osteopetrosis, a disease characterized by an increase in bone mass, due to a deficit in matrix degradation but not demineralization of hydroxyapatite. These knockout mice displayed osteopetrosis of the long bones and vertebrae as well as abnormal joint morphology (M. Gowen et al., J. Bone Miner Res. 1999, 14, 1654). The phenotype of the cathepsin K knockout mice resembles the human genetic disorder pycnodysostosis which is due to a mutation in the cathepsin K gene (W-S Hu et al., Journal of Clinical Investigation, 1999, 103, 731; B. D. Gelb et al, Science, 1996, 273, 1236). Patients with this disease have short, dense bones. These and other findings suggest that cathepsin K may play an important role in diseases involving bone resorption, excessive bone loss or cartilage or bone matrix degradation including osteoporosis (D. S Yamashita et al, Current Pharmaceutical Design, 2000, 6, 1), Gaucher disease (M. T. Moran et al, Blood, 2000, 96, 1969), Paget's disease, gingivitis, and periodontitis (G. A. Rodan et al, Science, 2000, 289, 1508), and rheumatoid arthritis (K. M. Hummel et al, J. Rheumatol., 1998, 25, 1887) (also see for example H. A. Chapman et al, Annu. Rev. Physiol., 1997, 59, 63; M. Gowen, Exp. Opin. Invest. Drugs, 1997, 6, 1199; and W. W. Smith et al., Exp. Opin. Ther. Patents, 1999, 9, 683).
The inhibition of cathepsin K has been described by B. D. Gelb et al (U.S. Pat. No. 5,830,850) as a method to ameliorate symptoms caused by bone resorption disorders, including osteoporosis, arthritides and periodontal disease, and damage caused by macrophage-medicated inflammatory processes. Studies in breast cancer research have shown that invading breast cancer cells have expressed low levels of Cathepsin K suggesting that these tumor cells may be able to directly resorb bone by the release of Cathepsin K. Inhibition of Cathepsin K may play a role in the metastatic potential and course of the disease (A. J. Littlewood-Evans et al, Cancer Research, 1997, 57, 5386). Increases in bone resorption and demineralization of bone are skeletal complications associated with many cancers and with bone metastases of breast and prostate tumors (G. A. Rodan et al, Science, 2000, 289, 1508). Cathepsin K has also been observed in giant cell aortitis suggesting that disorders associated with excessive elastin degradation such as lymphangiomyomatosis, vascular inflammation, and cardiovascular disease such as atherosclerosis may be attenuated with Cathepsin K inhibitors (H. A. Chapman et al, Annu. Rev. Physiol., 1997, 59, 63; D. S Yamashita et al, Current Pharmaceutical Design, 2000, 6, 1; and G. K. Sukhova et al, J. Clin. Invest., 1998, 102, 576).
Cathepsin S plays a key role in regulating antigen presentation and immunity (H. A. Chapman, 1998, Current Opinion in Immunology, 10, 93; R. J. Riese et al., 1998, J. Clin. Invest., 101, 2351; R. J. Riese et al., 1996, Immunity, 4, 357). Cathepsin S deficient mice have impaired invariant chain degradation resulting in decreased antigen presentation and germinal center formation, and diminished susceptibility to collagen-induced arthritis indicating the therapeutic potential for a cathepsin S inhibitor (G. Shi et al., 1999, Immunity, 10, 197; T. Y. Nakagawa et al, 1999, Immunity, 10, 207).
Control of antigen-specific immune responses has long been desirable as a useful therapy for autoimmune diseases. Such diseases include Crohn's disease, rheumatoid arthritis, and Multiple Sclerosis, as well as other T-cell-mediated immune responses (C. Janeway and P. Travers, 1996, Immunobiology, The Immune System in Health and Disease, Chapter 12). Furthermore, cathepsin S, which has broad pH specificity, has been implicated in a variety of other diseases involving extracellular proteolysis, such as Alzheimer's disease (U. Muller-Ladner et al., 1996, Perspectives in Drug Discovery and Design, 6, 87), atherosclerosis (G. K. Sukhova et al., 1998, J. Clin. Invest., 102, 576) and endometriosis (WO 9963115, 1999). A cathepsin S inhibitor has been found to block the rise in IgE titers and eosinophil infiltration in the lung in a mouse model of pulmonary hypersensitivity, suggesting that cathepsin S may be involved in asthma (R. J. Riese et al., J. Clin. Investigation, 1998, 101, 2351). Cathepsin inhibitors such as Leupeptin and E-64 were shown to have positive effects in a murine model of emphysema (J. A. Elias et al., J. Clin. Investigation, 2000, 106, 1081).
Another cysteine protease, cathepsin F has been found in macrophages and is also involved in antigen processing. It has been postulated that cathepsin F in stimulated lung macrophages and possibly other antigen presenting cells could play a role in airway inflammation (G.-P. Shi et al., J. Exp. Med., 2000, 191, 1177).
Cysteine proteases are characterized by having a cysteine residue at the active site which serves as a nucleophile. The active site also contains a histidine residue. The imidazole ring on the histidine serves as a base to generate a thiolate anion on the active site cysteine, increasing its nucleophilicity. When a substrate is recognized by the protease, the amide bond to be cleaved is directed to the active site, where the thiolate attacks the carbonyl carbon forming an acyl-enzyme intermediate and cleaving the amide bond, liberating an amine. Subsequently, water cleaves the acyl-enzyme species regenerating the enzyme and liberating the other cleavage product of the substrate, a carboxylic acid.
Inhibitors of cysteine proteases contain a functionality that can react reversibly or irreversibly with the active site cysteine. Examples of reactive functionalities that have been described (D. Rasnick, 1996, Perspectives in Drug Discovery and Design, 6, 47) on cysteine protease inhibitors include peptidyl diazomethanes, epoxides, monofluoroalkanes and acyloxymethanes, which irreversibly alkylate the cysteine thiol. Other irreversible inhibitors include Michael acceptors such as peptidyl vinyl esters and other carboxylic acid derivatives (S. Liu et al., J. Med Chem., 1992, 35, 1067) and vinyl sulfones (J. T. Palmer et al., 1995, J. Med Chem., 38, 3193).
Reactive functionalities that form reversible complexes with the active site cysteine include peptidyl aldehydes (R. P. Hanzlik et al., 1991, Biochim. Biophys. Acta., 1073, 33), which are non-selective, inhibiting both cysteine and serine proteases as well as other nucleophiles. Peptidyl nitrites (R. P. Hanzlik et al., 1990, Biochim. Biophys. Acta., 1035, 62) are less reactive than aldehydes and therefore more selective for the more nucleophilic cysteine proteases. Various reactive ketones have also been reported to be reversible inhibitors of cysteine proteases (D. Rasnick, 1996, ibid). In addition to reacting with the nucleophilic cysteine of the active site, reactive ketones may react with water, forming a hemiketal which may act as a transition state inhibitor.
Inhibitors of cathepsin K have been reported in the literature. D. S. Yamashita et al., (J. Am. Chem. Soc., 1997, 119, 11351) described 1,3-diamino-2-propanone inhibitors. S. K. Thompson et al. (Proc. Natl. Acad. Sci. USA, 1997, 94, 14249) described bis-aza analogs of these propanones as well as an aza-thiazole derivative. Introduction of a conformational constraint to the 1,3-diamino-2-propanones has led to 3-amido-pyrrolidin-4-one derivatives, 4-amido-piperidin-3-one derivatives, and eventually to azapanone-based inhibitors of Cathepsin K, as reported by R. W. Marquis et al. (J. Med. Chem. 1998, 41, 3563; J. Med. Chem. 2001, 44, 725; J. Med. Chem. 2001, 44, 1380). R. W. Marquis et al. (Bioorg. and Med. Chem. Letters, 1999, 7, 581) described peptidic alkoxymethylketones and thiomethylketones as cathepsin K inhibitors. Peptidyl vinyl sulfone cathepsin K inhibitors were described by L. Xia et al. (Biological Chem., 1999, 380, 679). Peptide aldehyde inhibitors of cathepsin K were reported by B. J. Votta et al. (J. Bone & Mineral Res., 1997, 12, 1396). J.-P. Falgueyret et al. (J. Med. Chem. 2001, 44, 94-104) described non-peptidic cyanamides as potent Cathepsin K inhibitors. T. Gamble et al. (49th Annual American Society for Mass Spectrometry Conference, May 27-31, 2001, Chicago, Ill.) described in vitro metabolism studies on cyanamide-containing Cathepsin K inhibitors. D. F. Veber has discussed numerous inhibitors of Cathepsin K including the following: 1,5-diacylcarbohydrazides (Biochemistry, 1999, 38, 15893; J. Med. Chem. 1998, 41, 3923), conformationally constrained 1,3-diamino ketones (J. Med. Chem. 1998; 41, 3563), and 1,3-bis(acylamino)-2-butanones, (J. Combinatorial Chem. 1999, 1, 207; J. Am. Chem. Soc. 1998, 120, 9114; J. Am. Chem. Soc. 1997, 119, 11351).
Examples of cathepsin S inhibitors have been reported. J. L. Klaus et al. (WO 9640737) described reversible inhibitors of cysteine proteases including cathepsin S, containing an ethylene diamine. In U.S. Pat. No. 5,776,718 to Palmer et al. there is disclosed in it's broadest generic aspect a protease inhibitor comprising a targeting group linked through a two carbon atom chain to an electron withdrawing group (EWG). The compounds of the present application are structurally distinct and are thus excluded from the disclosure in the U.S. Pat. No. 5,776,718. Other examples of cathepsin S inhibitors have been reported by E. T. Altmann et al, (WO 9924460, 1999) which describes dipeptide nitrites asserted to have activity as inhibitors of Cathepsins B, K, L and S. The WO publication does not disclose any compounds possessing a carboxylate linkage, Y—C(O)—O—, and fails to provide any description, methods or examples for particular spiroheterocylic moieties at the P1 position.
Certain acetamido acetonitrile derivatives have been disclosed by Tucker et al. (WO 00/49007) as inhibitors of cathepsin S and L. This WO publication likewise does not disclose or suggest any compounds possessing the carboxylate linkage, Y—C(O)—O—, as in the novel compounds according to the present invention.
Certain other cathepsin inhibitors have recently been disclosed by Marquis et al., WO 00/38687 and WO 00/39115; Altmann et al, WO 00/48993; Buysse et al., WO 00/55124; Singh et al, WO 00/59881 and Cowen et al. (WO 01/87828). Cathepsin inhibitors containing a cyclic cyanamide functionality were described by P. Prasit et al. (WO 01/77073). The compounds of the present invention are structurally distinct from the compounds disclosed in the aforementioned references.
Additional peptidyl nitrites have been reported as protease inhibitors. For example, both nitrites and ketoheterocycles are described by B. A. Rowe et al. (U.S. Pat. No. 5,714,471) as protease inhibitors useful in the treatment of neurodegenerative diseases. Peptidyl nitrites are reported by B. Malcolm et al. (WO 9222570) as inhibitors of picornavirus protease. B. J. Gour-Salin (Can. J. Chem., 1991, 69, 1288) and T. C. Liang (Arch. Biochim. Biophys., 1987, 252, 626) described peptidyl nitrites as inhibitors of papain.
A reversible inhibitor presents a more attractive therapy than irreversible inhibitors. Even compounds with high specificity for a particular protease can bind non-target enzymes. An irreversible compound could therefore permanently inactivate a non-target enzyme, increasing the likelihood of toxicity. Furthermore, any toxic effects resulting from inactivation of the target enzyme would be mitigated by reversible inhibitors, and could be easily remedied by modified or lower dosing. Finally, covalent modification of an enzyme by an irreversible inhibitor could potentially generate an antibody response by acting as a hapten.
In light of the above, there is a clear need for compounds which reversibly and selectively inhibit cysteine proteases such as cathepsin K and cathepsin S for indications in which these proteases exacerbate disease.